One of Assessee(proprietorship concern) is the trade partner of a Big Telecom company , He recieved interim payment for Activation commission in 2 or 3 insttalment during the month & issued Invoice in next month (ie. in April for the month of March) due to the data is provided by the company in next month & remaing amount paid after Invoicing by the company , so in context of new provision of payment of service tax , when the liability of payment of service tax will be arrise. & what would be the accounting tratment for the month of march-12